From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp1.linux-foundation.org (smtp1.linux-foundation.org [140.211.169.13]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "smtp.linux-foundation.org", Issuer "CA Cert Signing Authority" (verified OK)) by ozlabs.org (Postfix) with ESMTPS id EF7ABB70CE for ; Fri, 13 Aug 2010 05:08:30 +1000 (EST) Date: Thu, 12 Aug 2010 12:08:16 -0700 From: Andrew Morton To: Nathan Fontenot Subject: Re: [PATCH 0/8] v5 De-couple sysfs memory directories from memory sections Message-Id: <20100812120816.e97d8b9e.akpm@linux-foundation.org> In-Reply-To: <4C60407C.2080608@austin.ibm.com> References: <4C60407C.2080608@austin.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Cc: linuxppc-dev@ozlabs.org, Greg KH , linux-kernel@vger.kernel.org, Dave Hansen , linux-mm@kvack.org, KAMEZAWA Hiroyuki List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Mon, 09 Aug 2010 12:53:00 -0500 Nathan Fontenot wrote: > This set of patches de-couples the idea that there is a single > directory in sysfs for each memory section. The intent of the > patches is to reduce the number of sysfs directories created to > resolve a boot-time performance issue. On very large systems > boot time are getting very long (as seen on powerpc hardware) > due to the enormous number of sysfs directories being created. > On a system with 1 TB of memory we create ~63,000 directories. > For even larger systems boot times are being measured in hours. And those "hours" are mainly due to this problem, I assume. > This set of patches allows for each directory created in sysfs > to cover more than one memory section. The default behavior for > sysfs directory creation is the same, in that each directory > represents a single memory section. A new file 'end_phys_index' > in each directory contains the physical_id of the last memory > section covered by the directory so that users can easily > determine the memory section range of a directory. What you're proposing appears to be a non-back-compatible userspace-visible change. This is a big issue! It's not an unresolvable issue, as this is a must-fix problem. But you should tell us what your proposal is to prevent breakage of existing installations. A Kconfig option would be good, but a boot-time kernel command line option which selects the new format would be much better. However you didn't mention this issue at all, and it's the most important one. > Updates for version 5 of the patchset include the following: > > Patch 4/8 Add mutex for add/remove of memory blocks > - Define the mutex using DEFINE_MUTEX macro. > > Patch 8/8 Update memory-hotplug documentation > - Add information concerning memory holes in phys_index..end_phys_index. And you forgot to tell us how long those machines boot with the patchset applied, which is the entire point of the patchset!